1. Field of the Invention
This invention relates to a process for bonding magnesium phosphate cementitious materials to base materials and is more particularly concerned with the process for improving the bond between such materials by precoating the surface of the base material with a passivating agent, and with the resulting laminated structures.
2. Related Information
The problem of applying cementitious material as an overlay to various base materials e.g., monolithic concrete and the like, is a difficult one, and none of the solutions heretofore suggested have been entirely satisfactory. It is well known, for example, that one cannot successfully apply an overlay, a coating or layer of a cementitious material to a set concrete base because the overlay or finishing coat cracks and does not form a firm permanent bond between the concrete base and the applied overlay or coating. This problem is compounded when the cementitious material is appreciably different, e.g., chemically, from the base material. Thus, the problem of developing a process for satisfactorily applying cementitious materials to base structural materials is a very real one in this art.
The method most commonly used heretofore is that of applying an adhesive coating to the base material or substrate, which coating is in the nature of an asphalt emulsion. Over this adhesive coating is applied the cementitious material. It is necessary to apply the cementitious material immediately after application of the adhesive coating, since the action depends on the tack qualities of the adhesive. In the course of time, such finish coatings applied according to that process crack and craze because of the deterioration of the underlined film of asphalt, a material notoriously susceptible to oxidation, temperature changes and internal breakdown of the constituents thereof.
U.S. Pat. No. 2,200,433 (Ripley, May 14, 1940) discloses methods of resurfacing concrete roadways. In this process the roadway is first treated with a relatively concentrated solution of caustic alkali which serves to facilitate suponification and removal of any organic film. The alkali is next removed, for example, by sweeping the road surface, and hydrochloric acid is sprayed or otherwise applied to the road surface. Other acids can replace hydrochloric acid, such as sulfuric or the like, but hydrochloric acid is preferred. Next, a thin layer of sodium orthoborate is applied to the road surface prior to the application of a mixture of cement and water or a mixture of sand, cement and water as a dressing surface. The layer of sodium orthoborate/acid mixture on the road surface will facilitate bonding of the dressing layer with the concrete road surface. This reference neither discloses the various passivating agents useful in this invention nor the use of a magnesium phosphate cementitious material. It is also noted that borates are not effective passivating agents in the process of this invention.
U.S. Pat. No. 2,954,301 (Szukiewicz, Sept. 27, 1960) discloses a process for bonding freshly applied hydraulic cement materials, e.g., Portland cement, magnesium aluminate cement, so-called magnesium oxychloride cement, concrete made from such cements, and plasters of Paris to surfaces of a similar character. This process comprises coating the old cement surface with a mixture containing an adduct prepared by reacting a polyol with an organic polyisocyanate and a resin-forming catalyst, curing the resulting coating by exposure to the atmosphere until the coating becomes dry and tacky, applying fresh water-containing hydraulic cement material to the dry and tacky coating and permitting the water-containing hydraulic material to form a strong bond with the old cement surface. This reference does not disclose the passivating agents useful in the present invention.
U.S. Pat. No. 3,984,269 (Schneller et al., Oct. 5, 1976) discloses a process for accelerating the set of a settable dry wall joint compound by the use of a layer of set accelerator beneath and on top of each coat of settable compound. The set accelerator is a spray application of a thin coat of aluminum sulfate. The joint compound comprises a settable calcined gypsum binder. Set accelerators can also include the sulfate of calcium, magnesium, potassium, cadmium, copper, sodium, iron, chromium and ammonium, potassium aluminum sulfate, sodium hydrogen sulfate, zinc acetate, potassium bichromate, ferric chloride, sulfuric acid and oxalic acid. These other accelerators provide a lesser degree of function than the preferred aluminum sulfate. This reference neither discloses the variety of passivating agents nor the cementitious and base materials contemplated by this invention.
U.S. Pat. No. 4,367,247 (Akerberg, Jan. 4, 1983) discloses a primer composition for Portland cement concrete comprising the reaction product of polyphosphoric acid and an alcohol. This primer composition improved the bonding between Portland cement concrete and the resinous coating materials used to protect the surface of the cement. The cementitious material overlying the base material of this invention does not include the resinous coating, e.g. furan resins, contemplated by this reference.
Surface Preparation of Concrete for Paints and Coating by Robert W. Gaul, reprinted from Concrete Construction Magazine, World of Concrete Center, 426 S. Westgate, Addison, Ill. disclosed that although acid etching has been widely used to remove laitance or dirt from concrete, it is not a preferred method because it is difficult to control, especially in assuring that all of the acid and residue are cleaned from the surface. A 10% solution of hydrochloric acid or a 15% solution of phosphoric acid can be used to acid etch. After the surface is acid etched, it is throughly flushed with water, scrubbed with stiff brooms, and then allowed to dry before a coating is applied. The coatings applied, usually paints, can be to decorate the surface, to dampproof, to waterproof or otherwise to protect the Portland cement concrete surface. This reference neither discloses the passivating agents nor the cementitious material of this invention.
U.S. Pat. No. 2,976,173 (Czerwin et al., March 21, 1961) discloses a processes for improving the bond between concrete, plaster or the like to surfaces of concrete or other hydraulic material by precoating the surface of the base material with polyvinyl alcohol. This reference does not disclose the use of the passivating agents of this invention.
U.S. Pat. No. 2,760,885 (Larsen et al., Aug. 28, 1956) discloses a process for bonding hydraulic cementitious materials. In this process the base material is coated with a film of aqueous emulsion of a resin, the deposited solids of which will reemulsify on contact with water. The coating resin can be polyvinyl acetate alone or in combination with either xylene glycol alone or in combination with tricresyl phosphate. This reference does not discloses the passivating agent of this invention.